This invention relates to a polishing cloth for texturing the surface of a magnetic hard disk substrate by using free abrading particles and a method of texturing by using such a cloth.
In general, the texturing of the surface of a disk substrate, say, of an aluminum alloy by means of free abrading particles is carried out by pressing a polishing cloth on the target surface to be polished while supplying liquid slurry serving as the free particles onto the surface and rotating the disk substrate while adjusting the pressure on the polishing cloth. The liquid slurry may be one obtained by mixing abrading particles of aluminum oxide, silicon carbide or diamond with an aqueous solution containing a surfactant and stirring the mixture together. In the past, woven cloths produced by weaving plastic fibers were frequently used for such a texturing process. Such a cloth may be produced, for example, by weaving both longitudinally and transversely woven bundles of plastic fibers of polyester or tetron and cut in the shape of a circle or a tape.
With the recent increase in the memory capacity of magnetic hard disks, there is a demand to increase the density of various memory media. As a result, it has become necessary to reduce and stabilize the floating distance of a magnetic head over the surface of a magnetic hard disk substrate and the surface texturing on such disk surfaces is required to be ever finer and more uniform than before. By a texturing process with the use of free abrading particles and a polishing cloth as described above, however, abnormal protrusions, waviness and irregular patches are generated on the textured surface and it was not possible to carry out a fine and uniform texturing of a surface of a magnetic hard disk substrate. In other words, it has been very difficult to reduce and stabilize the floating distance of a magnetic head, and this has been a cause of collisions or adhesion between the magnetic head and a hard disk.
Next will be explained the reasons for finding abnormal protrusions, waviness and patches on a textured surface of a magnetic hard disk substrate. FIG. 2 shows the conditions of a polishing surface of a conventional polishing cloth 20 produced by weaving woven bundles 23 of plastic fibers longitudinally and transversely to serve as its base 21 having a polishing surface 22. As can been seen in FIG. 2(a) in which a small portion B of the polishing surface 22 is enlarged, the polishing surface 22 of a prior art polishing cloth 20 has many protrusions and indentations. If a polishing cloth with such protrusions and indentations on its polishing surface is used in a texturing process by means of free abrading particles, the target surface to be polished experiences compressive forces of different magnitude, depending on whether it is being pressed by one of the protrusions or indentations on the surface of the polishing cloth. The liquid slurry which is supplied onto the target surface will not be pressed uniformly, and patches are finally left on the finished surface. As a result, abnormal protrusions may be formed on the surface of the disk substrate or waviness may be generated. Grooved lines cannot therefore be formed at a high density, and it is concluded that prior art polishing cloth is not suited for a fine and uniform texturing process.
With the recent increase in the demand for magnetic hard disks, it is also coming to be severely required to shorten the time spent for the texturing of magnetic hard disk substrates and to thereby increase the throughput.